Mosquito season is back, and so is West Nile Virus (WNV). Each summer, the virus re-emerges across parts of Canada, cycling between mosquitoes and birds, with occasional spillover into humans and other animals1,2. As the 2026 West Nile season progresses, the CWHC Ontario/Nunavut branch is tracking the virus in wild birds and what these detection patterns could mean for wildlife and human health.
West Nile Virus (WNV) is a mosquito-borne disease that is dispersed globally and maintained through mosquito-bird-mosquito transmission cycles2. Corvids, such as crows, ravens, and jays, as well as hawks, owls, and other raptors are highly susceptible to WNV infection2,6. These birds often die as a result of infection, making them valuable indicators of virus activity. Humans and horses are susceptible as well, however, the majority of infected people never develop symptoms, and severe illness is uncommon (about 20% of infected people experience mild to moderate symptoms of febrile illness, and less than 1% may experience conditions affecting the nervous system) 1, 4. Although mosquito bites are the primary route of transmission, infection can also rarely occur through blood transfusions, organ transplants, and breast feeding5. Hot temperatures and rain in early summer create favorable conditions for mosquito populations. Therefore, the virus remains a concern until mosquito activity declines (often after the first hard frost)5.
Wildlife surveillance, such as testing deceased birds, provides an important early indicator of West Nile virus activity and disease risks for humans and domestic animals2. The CWHC’s Ontario/Nunavut branch detects the majority of infected birds later in the summer months. However, in more recent years, our first detections of WNV in wild birds are regularly occurring in April and May, likely associated with warmer spring temperatures which favour early mosquito emergence1. So far in 2026, our region confirmed three wildlife specimens with WNV in May, twelve in June, and twenty in July. All confirmed cases have been in corvids, highlighting their importance in West Nile virus activity monitoring.
Protect Yourself from Mosquito Bites
You can’t tell whether a mosquito is carrying West Nile virus just by looking at it, so taking a few precautions can help reduce your risk:
- Use an insect repellent containing DEET, picaridin, or IR3535
- Wear light-coloured, tightly woven clothing with long sleeves and pants when outdoors
- Limit outdoor activity during dusk and dawn, when mosquitoes are most active
- Remove standing water sources around your home, including clogged gutters, planters, or other containers where mosquitoes can breed 3,4,6
For more information on West Nile virus and prevention, visit the Government of Ontario and the Public Health Agency of Canada.
Wildlife surveillance remains an important tool for monitoring West Nile virus activity and protecting both wildlife and human health 2,6. Members of the public play an important role in contributing to WNV surveillance. If you find a dead bird in Ontario, especially a corvid, please contact the CWHC by phone (toll free) at 1-866-673-4781 or by submitting an online report at https://cwhc.wildlifesubmissions.org/.
Written By Kaitlyn Young and Fenn Woodstock
References
- Albrecht, L., & Kaufeld, K. A. (2023). Investigating the impact of environmental factors on West Nile virus human case prediction in Ontario, Canada. Frontiers in Public Health, 11, Article 1100543. https://doi.org/10.3389/fpubh.2023.1100543
- Gould, C. V., Staples, J. E., Guagliardo, S. A. J., Martin, S. W., Lyons, S., Hills, S. L., Nett, R. J., & Petersen, L. R. (2025). West Nile Virus: A Review. JAMA : The Journal of the American Medical Association, 334(7), 618–628. https://doi.org/10.1001/jama.2025.8737
- Ministry of Health. (2023). West Nile Virus Preparedness and Prevention Plan. King’s Printer for Ontario. https://files.ontario.ca/moh-ophs-ref-west-nile-virus_plan-2023-en.pdf
- NCCID. (2022). West Nile virus. National Collaborating Centre for Infectious Diseases. https://nccid.ca/debrief/west-nile-virus/
- Todoric, D., et al. (2022). An overview of the National West Nile Virus Surveillance System in Canada: A One Health approach. Canada Communicable Disease Report. 48 (5). https://pmc.ncbi.nlm.nih.gov/articles/PMC10262935/
- World Health Organization. (2017). West Nile virus. https://www.who.int/news-room/fact-sheets/detail/west-nile-virus